Efficient and productive recovery of oil and natural gas from underground deposits involves several complex technologies. For example, primary recovery relies on underground pressure, which can originate from several sources including an underlying water layer below the oil layer or a gas cap formed of gas collected immediately above the oil layer. Whether or not such underground pressure initially existed, once reservoir pressure has either been depleted or is otherwise below a minimum value, oil must be brought to the surface using secondary methodologies. One such secondary methodology includes injecting water below the oil layer. Another methodology includes injecting a gas above the oil layer. Other methodologies of extracting oil, particularly when underground pressure has been depleted to a point where the reservoir cannot be sufficiently pressurized, include reducing the viscosity through the injection of heat, vapor, surfactants, solvents, or miscible gases (e.g., carbon dioxide).
Water is a particularly useful tool because it can be used to pressurize a virgin or depleted reservoir (both naturally and through injection), but can also be used to proactively maintain reservoir pressure and/or to direct oil in a reservoir toward an existing oil well. While production wells can be converted into injection wells, water-injection wells are also drilled specifically for the purpose of enhanced oil recovery. Water is then pumped into the reservoir, or gravity can help to push the liquid into the formation. Performance of water injection wells is monitored to ensure desired operation of the oil recovery process. When an obstruction forms in the wellbore, effective detection and estimation techniques are needed to characterize and remove such obstruction. Obstructions usually result from deposits in the wellbore, for example, scale paraffin, asphlatenes, salt, solids or corrosion products. Obstructions can also result from debris or particles in the injected fluid. Obstructions can also result from build-up of fines and scale in the wellbore. Obstructions can also result from mechanical downhole fish issues such as those resulting from items left in a wellbore, including, but not limited to, pieces of various drilling, logging, or production equipment. Deformations in the tubing or casing of the wellbore can also cause obstructions. These obstructions can be removed or reduced by one or more of chemical and mechanical technologies, depending on several factors including location of the obstruction and its properties. A chemical technology often used in treating obstructions involves acid treatments. Various acids, such as sulfuric acid and hydrochloric acid, have been injected into the wellbore in order to remove blocking material and to increase the productivity of injection wells. Obstructions can also be removed or decreased in size by mechanical milling using coiled tubing or wireline or other specialized apparatuses.